The present invention relates to a technique for discriminating cylinders at a predetermined stroke of an engine, and particularly relates to a technique for discriminating cylinders as soon as possible after start of cranking.
As the conventional cylinder discrimination device, there is known such a device in which cylinder discrimination signals of the number corresponding to the number of cylinders are output from a cam sensor during an output of a reference crank angle signal from a crank angle sensor, to perform cylinder discrimination (Japanese Unexamined Patent Publication No. 5-106500).
However, in an engine equipped with a valve timing control device for detecting a rotation phase of a camshaft relative to a crankshaft to perform successively a variable control of the rotation phase, there is a need to detect a crank angle position for each unit crank angle to a reference crank angle position only by a crank angle signal output in synchronization with rotation of the crankshaft. Therefore, to generate and detect the reference crank angle signal in another line separately from the unit crank angle signal requires the cost and space, since two crank angle sensors are substantially disposed and two a signal processing systems are needed. When the reference crank angle signal is mixed with a signal for each unit crank angle, the detection of the reference crank angle becomes difficult. There is a system to detect the reference crank angle position based on a cycle ratio between prior and post signals as a structure to ignore the unit crank angle signal at a position corresponding to the reference crank angle position.
However, in such a system to detect the reference crank angle position with the cycle ratio and the like, when the engine rotation immediately after a cranking start is in an unstable state, it is difficult to accurately detect the reference crank angle position, and the detection becomes possible at a second reference crank angle position. Consequently, cylinder discrimination becomes possible based on the number of cylinder discrimination signals between a first cylinder discrimination timing and the next cylinder discrimination timing detected by the detection of the reference crank angle position. Namely, at the second cylinder discrimination timing to be detected after the cranking start (=the third cylinder discrimination timing if the first cylinder discrimination timing impossible to be detected is included), the cylinder discrimination is possible for the first time.
When the cylinder discrimination is delayed as above, a fuel is wastefully injected without combustion, resulted in deterioration of an engine start performance and an exhaust emission.
The present invention has been achieved taking into consideration the above mentioned problems and has an object to enable cylinder discrimination to be performed as soon as possible after a cranking start.
Especially, for an engine equipped with a valve timing control device for successively performing a variable control of valve timings of an intake valve and an exhaust valve by successively performing a variable control of rotation phase of a camshaft relative to a crankshaft, cylinder discrimination can be performed as soon as possible after a cranking start.
To achieve the above object, the present invention is constituted as follows.
A crank angle signal is output, at a crank angle position for each unit crank angle using a reference crank angle position for each stroke phase difference between cylinders as a reference, from a sensor mounted to a member interlocked with a crankshaft in synchronization with the rotation of the crankshaft.
From a sensor mounted to a member interlocked with a camshaft, different numbers of cylinder discrimination signals are output, depending on cylinders to be discriminated, during a predetermined crank angle period for each stroke phase difference between cylinders.
A counter or a memory counts the number of crank angle signals output after a cranking start and holds a count value of each time the cylinder discrimination signal is output.
A computation processing unit (CPU) compares the count value of the number of crank angle signal outputs at a first cylinder discrimination timing with the past count value held, and detects the number of cylinder discrimination signals output during the predetermined crank angle period, to perform first cylinder discrimination after the cranking start based on the number of the cylinder discrimination signals.
In this way, each time the cylinder discrimination signal after the cranking start is output, the count value of the number of the crank angle signal outputs is held. Among these held count values, the count value which has a difference within a certain value to the count value in the cylinder discrimination timing can be judged to have been obtained because the cylinder discrimination signal is output during the predetermined crank angle period. As a result, the number of cylinder discrimination signals output during the predetermined crank angle period is detected so that cylinder discrimination can be performed.
Accordingly, even if the first cylinder discrimination timing cannot be detected at that point after the cranking start, at a second cylinder discrimination timing the cylinder discrimination can be accurately performed, thereby enabling to improve the engine start performance and the exhaust emission performance by quick cylinder discrimination.
Further, the constitution may be such that, as the past count values, a plurality of count values including the latest renewed value and the values prior to the latest renewed value are held, and based on a value obtained by subtracting each past count value from the count value at the first cylinder discrimination timing, the number of the cylinder discrimination signals output during the predetermined crank angle period is detected.
According to the above constitution, only by holding the number of count values of the crank angle signals required for the cylinder discrimination, the cylinder discrimination can be performed by detecting the number of cylinder discrimination signals output during the predetermined crank angle period, based on the value obtained by subtracting each past count value from the count value at the first cylinder discrimination timing.
It is preferable that a detection of the reference crank angle position may be prohibited until a predetermined number of the crank angle signals after the cranking start is output.
In a case of a first reference crank angle position after the cranking start, even if the first cylinder discrimination timing is detected based on the detection of the reference crank angle position, since the predetermined crank angle period capable of the cylinder discrimination has not elapsed, the cylinder discrimination can not be performed. Further, since the engine rotation is unstable immediately after the cranking start, there is a possibility of erroneous detection of the reference crank angle position.
Therefore, until the predetermined number of crank angle signals after the cranking start is output, the detection of the reference crank angle position is prohibited, so that an erroneous detection of the reference crank angle position can be prevented and the cylinder discrimination can be accurately performed at the first cylinder discrimination timing based on the detection of the first reference crank angle position.
Preferably, if the count value of the crank angle signals when detected a cylinder discrimination timing after the cranking start does not reach the count value of when the predetermined crank angle period has elapsed, the cylinder discrimination at the cylinder discrimination timing is prohibited.
If, after a cranking start, the detection of the reference crank angle position is not prohibited for the time being, and the count value of crank angle signals when detected the cylinder discrimination timing based on the detected reference crank angle position does not reach the count value of when the predetermined crank angle period has elapsed, there is a possibility that the cylinder discrimination cannot be performed normally and the reference crank position is detected erroneously. Therefore, at that stage, the cylinder discrimination is prohibited.
The other objects and features of the present invention will become understood from the following description with the accompanying drawings.